1. Field of the Invention
This invention relates in general to electrical connectors, and more particularly to a method and apparatus for providing compressive connection with electrostatic discharge dissipative properties.
2. Description of Related Art
Magnetic head-based systems have been widely accepted in the computer industry as a cost-effective form of data storage. In a magnetic disk drive system, a magnetic recording medium in the form of a disk rotates at high speed while a magnetic read/write transducer, referred to as a magnetic head, “flies” slightly above the surface of the rotating disk. The magnetic disk is rotated by means of a spindle drive motor. The magnetic head is attached to or formed integrally with a “slider” which is suspended over the disk on a spring-loaded support arm known as the actuator arm. As the magnetic disk rotates at operating speed, the moving air generated by the rotating disk in conjunction with the physical design of the slider lifts the magnetic head, allowing it to glide or “fly” slightly above and over the disk surface on a cushion of air, referred to as an air bearing. The flying height of the magnetic head over the disk surface is typically only a few tens of nanometers or less and is primarily a function of disk rotation, the aerodynamic properties of the slider assembly and the force exerted by the spring-loaded actuator arm.
In a magnetic tape drive system, a magnetic tape typically containing data tracks that extend along the length of the tape is drawn across magnetic tape heads. The magnetic tape heads can record data (with writing elements or writers) and read data (with read elements or readers) as relative movement occurs between the heads and the tape.
A major problem that is encountered during manufacturing, handling and use of magnetic recording transducers, referred to as heads, is the buildup of electrostatic charges on the various elements of a head or other objects which come into contact with the heads, particularly sensors of the thin film type, and the accompanying spurious discharge of the static electricity thus generated. Static charges may be produced whenever two materials are rubbed against one another. If the static charges are dissipated through the MR sensors, the sensors will heat up. If the sensor temperature is sufficiently high, it can be damaged magnetically or physically. If the changes to the sensor properties are minimal or reversible, then the process is called electrostatic overstress (EOS). If the changes to the sensor properties are irreversible, then the process is called electrostatic damage (ESD).
Magnetoresistive (MR) sensors, also referred to as “MR readers”, are particularly useful as read elements in magnetic heads, especially at high data recording densities. The MR sensor provides a higher output signal than an inductive read sensor. This higher output signal results in a higher signal-to-noise ratio for the recording channel and allows higher a real density of recorded data on a magnetic surface of the media.
As described above, when a sensor is exposed to electrostatic discharge or even a voltage or current input larger than that intended under normal operating conditions, the sensor and other parts of the head may be damaged. This sensitivity to electrical damage is particularly severe for MR read sensors because of their relatively small physical size. For example, an MR sensor used for extremely high recording densities will have a current carrying cross-sectional area of the order of 100 Angstroms (Å) by 1.0 micrometers (μm) or even smaller and lengths of the order of 1 to 10 μm. Discharge of voltages of only a few volts through such a physically small sensor, behaving like a resistor, are sufficient to produce current densities capable of severely damaging or completely destroying the MR sensor. The nature of the damage which may be experienced by an MR sensor varies significantly, including complete destruction of the sensor via melting and evaporation, resulting in an open circuit or a short or oxidation of the air bearing surface, and milder forms of physical or magnetic damage in which the head performance may be degraded.
The static build up of charge on materials used in the manufacturing of tape or disk drive heads should be avoided to minimize the potential of EOS or ESD damage to the heads.
Flexible cables are often used to electrically interconnect electrical devices such as circuit boards in an assembly, connectors on a circuit board, and other electrical devices that may experience relative motion. Flex strips are generally well-known in the art as multiple flat electrical conductors usually laid out in parallel strips and encased in a flexible, nonconductive material. The resulting flexible electrical interface, i.e., the flex strip, can be bent and twisted within limits. Often, electrical connection means are provided at either end of the conductive strip. For example, contact pads may be formed at the ends of the individual constructive strips and held in contact with mating contact pads on the electrical device.
Heads used in tape drives predominately use flexible cables which allow for electrical contact between the elements in the head and the external electrical circuits uses to communicate with the head and read signals from the head which are generated while reading magnetic information written onto the storage media (magnetic coated tape in particular). A means must be used to connect the electrical contacts in the flexible cable on the head with the external electronics devices. In particular, one type of compression connector used with MR heads used in tape storage drives. The compressive connector can be repeatably releasable, allowing testing of the MR heads during manufacturing or interchange in a product drive. The flexible cable will, in generally, have a plurality of electrical contacts on a surface of the cable. A matching circuitized flexible substrate is provided having electrical contacts on a facing surface that are arranged to match electrical contacts on the flexible cable when in a face-to-face relationship. An elastomeric compression element, which has a plurality of protruding compression members, is positioned at a rear surface of the matching circuitized flexible substrate with the protruding compression members facing and in contact with the rear surface, such that individual compression members are registered with corresponding individual electrical contacts. Elongated electrical contacts are registered with two adjacent individual compression members and a reference plate supports the elastomeric compression element. The electrical contacts are registered in face-to-face relation with matching electrical contacts of the circuitized flexible substrate and a force is exerted normal to the facing surface of the matching circuitized flexible substrate. The normal force causes compression of the elastomeric compression element between the matching circuitized flexible substrate and the reference plate to create non-wiping contact between the electrical contacts of the flexible cable substrate and the electrical contacts of the matching circuitized flexible substrate, thereby forming a releasable, repeatable electrical connection therebetween.
However, materials currently used in compressive connectors include a rubber material encased in a hard plastic, both of which are insulators. When pressure is applied to the rubber material, the rubber material charges up substantially. For example, the elastomer may routinely charge up to 1000 volts when pressure is applied or removed from the compression connection. This charge can result in damage to the sensitive electrical circuits for which the compression connection is used through ESD or EOS.
It can be seen then that there is a need for a method and apparatus for providing a compressive connection with electrostatic discharge dissipative properties.